A couple accused of murdering teenager Becky Watts had threesomes with another woman, a court has heard.

Nathan Matthews, 28, and Shauna Hoare, 21, had the consensual threesomes with a mutual friend on at least two occasions – with it being filmed on a mobile phone by Matthews, the Press Association reports.

He is accused of killing his 16-year-old stepsister with his girlfriend in a sexually motivated kidnap plot on February 19.

Nathan Matthews pictured with his girlfriend Shauna Hoare at a Christmas fancy dress party

The couple allegedly dismembered 5ft 1in Becky into eight parts, which were discovered in a garden shed 80 metres from their Bristol home on March 3.

The woman told the jury at Bristol Crown Court that the sexual activity took place at the beginning of 2014 at her home in Bristol with Matthews and Hoare.

Asked about it by prosecutor William Mousley QC, the woman broke down in tears and replied: "Yes... I am sorry..."